Minimally invasive procedures are increasingly being used by medical practitioners to diagnose and treat medical conditions. Compared to open surgery, minimally invasive procedures involve smaller incision sizes, resulting in less injury to patients, improved recovery times, and reduced complications. A growing number of procedures are performed minimally-invasively using an access point (e.g., an incision) positioned remotely from the site of diagnosis or treatment. For example, increasingly, cardiovascular procedures such as aortic valve repairs and vascular stent implantations are performed by entering the patient's vasculature via a small incision in the femoral artery.
Robotic surgical systems are well suited for minimally invasive medical procedures, because they provide a highly controllable yet minimally sized system to facilitate instrument navigation to areas that may lie deep within a patient. The Magellan® robotic catheter system manufactured by Hansen Medical Inc. (Mountain View, Calif.) is one such robotic surgical system; it includes a telescoping catheter system formed of an inner elongate member and an outer elongate member. Both the inner and outer members have multi-directional articulation capabilities. Such a system is described, for example, in U.S. Pat. No. 8,827,948. To navigate the robotic catheter using the system, the system's interface requires a user to direct the catheter's movement in multiple degrees of freedom. The user must direct axial translation (i.e., insertion and/or retraction) as well as an articulation angle magnitude (i.e., the bend) and articulation angle direction (i.e., the roll or roll plane) of both the inner and outer members. The user must also direct translation of a guidewire. While users can handle instrument navigation relatively well when navigating in a constrained space such as a narrow blood vessel, it becomes much more challenging to navigate in an organ, an ostium of a branch vessel, or other relatively open three-dimensional space. Navigation in such an open area forces the user to understand the three-dimensional relationship of the instrument relative to the anatomical target and determine in which plane the instrument will bend.
This task is difficult, in part, because navigating an instrument through a lumen of the patient from a remote patient access point to the desired site of a procedure requires manipulating the instrument without a direct line of sight of the instrument. A tracking system may be used to help locate the desired site of the procedure and visualize the navigation of the instrument to the desired site of the procedure. Tracking systems allow the user to visualize a patient's internal anatomy and the location and/or orientation of the instrument within the patient's anatomy.
Many visualization systems are not suitable for continuous real-time tracking of instruments though. For example, some systems such as positron emission tomography (PET), X-ray computed tomography (CT), and magnetic resonance imaging (MM) produce and combine many cross-sectional images of an object to generate a computer-processed image; such an image capture process is slow and movement within the photographed field during the image capture process produces image artifacts that make such systems unsuitable for real-time tracking of moving instruments in a body. Additionally, some visualization systems such as X-ray CT and fluoroscopy emit potentially harmful ionizing radiation, and the duration of their use should be limited when possible. Direct endoscopic imaging (e.g., with an intraluminal camera) is suitable for predominantly empty lumens such as the gastrointestinal tract but is not suitable for blood-filled vasculature.
Tracking systems such as electromagnetic (EM) tracking systems and fiber optic tracking systems provide a promising form of real-time instrument tracking. EM sensing functions by placing an EM sensing coil (i.e., an EM sensor) in a fluctuating magnetic field. The fluctuating magnetic field induces a current in the coil based on the coil's position and orientation within the field. The coil's position and orientation can thus be determined by measuring the current in the coil. A single EM sensor is able to sense its position and orientation in three-dimensional space with five degrees of freedom (i.e., in every direction except roll). That is, the EM sensor is able to sense orientation in every direction except around the axial symmetric axis of the coil. Two EM sensors held fixed relative to each other on an instrument may be used to sense all six degrees of freedom of the instrument. In a navigation system employing EM tracking, an image of an anatomical space is acquired, the position and orientation of one or more EM sensors on an instrument are detected, and the system uses a registration between an EM sensor frame of reference and an anatomical space frame of reference to depict movement of the tracked instrument within the imaged anatomical space. The use of EM sensors to track medical instruments and localize them to a reference image is described, for example, in U.S. Pat. Nos. 7,197,354 and 8,442,618. Fiber optic position tracking or shape sensing devices are described, for example, in U.S. Pat. No. 7,772,541. In one example of fiber optic position tracking, a multi-core optical fiber is provided within a medical instrument, with a light source coupled to one end of the optical fiber and a detector coupled to the opposing end. The detector is configured to detect light signals that pass through the optical fiber, and an associated controller is configured to determine the geometric configuration of at least a portion of the medical instrument based on a spectral analysis of the reflected portions of the light signals. With such tracking systems, a medical practitioner can, in theory, observe movements of the instrument on a display and adjust user inputs as needed to navigate the instrument to a target location.
In practice, users often struggle to navigate instruments to target locations with existing tracking systems. One cause of the problem is that, for flexible instruments such as catheters, their shape inside the anatomy adjusts to the shape of the anatomy as the instrument is inserted. This shape does not always adjust uniformly or in a manner that is simple to predict, in part, because the stiffness of a flexible instrument is not uniform along the instrument. For example, in a telescoping catheter, a proximal segment of the outer member is stiffer than its articulation section, and the stiffness of the inner member increases if a guidewire is inserted inside. This lack of uniformity and predictability can be problematic when inserting a flexible instrument into an anatomy, especially when using a tracking system with sensors that only track discrete point(s) on the instrument (such as EM tracking sensors). With such systems, it can be difficult to discern the entire shape of the instrument.
Users also struggle to navigate instruments to target locations because robotic catheter systems are not always intuitive to drive. With flexible instruments that navigate through the anatomy, the instrument's tip position does not always follow the commanded position. This may be due to distortion from contact with the anatomy or deformation of the instrument due to articulation and insertion forces. This creates difficulty in knowing the actual position of the instrument. Tracking and localization make knowledge of the instrument position in three dimensions more visible to the user, but many medical practitioners still struggle to navigate the instrument to the desired anatomical target even when a live-tracked instrument is displayed over an image of the anatomy.
The struggle is largely due to the nature of the two-dimensional information being displayed to the practitioners. Some imaging systems have incorporated 2-D/3-D image fusion systems, for example, as described in U.S. Pat. No. 5,672,877. In one example, a fluoroscopic system can receive a pre-operative three-dimensional dataset from a CT or MRI and acquire two-dimensional images of the organ cavity or portion of the patient undergoing the interventional procedure. These systems can then generate a 3-D/2-D fusion visualization of the organ cavity or portion of the patient based on the acquired two-dimensional image and the three-dimensional image dataset. The three-dimensional image dataset is registered to the two-dimensional image. The three-dimensional image dataset and the two-dimensional image are then displayed as a 3-D/2-D fusion visualization, providing a 3-D model. However, even if a three-dimensional model is provided to help a user visualize the instrument in space, the instrument representation is ultimately projected onto a screen in two dimensions. Many users find it difficult to “think in three dimensions” (i.e., mentally convert two-dimensional images into the three-dimensional model).
Accordingly, there is a need for new and useful robotic systems that combine the capabilities of 3-D imaging and 3-D tracking while addressing the unique challenges of flexible instruments to assist users in navigating instruments within the human body.